Cursor Open-Sources Mixture-of-Kittens (MoK): A Deterministic MoE Training Megakernel for GB300 NVL72 Racks

1Key Takeaways

• Cursor Research has open-sourced Mixture-of-Kittens (MoK), the MoE training megakernel behind its Composer models.
• MoK fuses all mixture-of-experts communication and computation into a single deterministic kernel, and runs up to 2.37x faster than the strongest public baseline on GB300 NVL72 racks.
• It requires Blackwell SM100 or SM103 GPUs, which puts it out of reach for anyone without NVL72 capacity.